The conventional structure of a supporting frame of any type is commonly constructed by angle irons (as shown in FIG. 1) as the assembly units. At both sides of the angle iron, two series of screw hole are evenly provided to enable a plurality of screws to secure the angle irons with each other to form the supporting frame. The adjustability of the frame is thus limited to the space between each screw hole provided on the angle iron, so that fine adjustment is impossible and not all the height requirement can be met. Moreover, when the user needs to re-adjust the height of the supporting frame, he or she must entirely unscrew all the connection screws to release all the lateral angle irons from the vertical angle irons and rescrew them to the vertical angle irons at desired height again. The adjusting operation is time consuming and really troublesome.
Since metal is the most common construction material for framework, after a certain period of time, rust may easily form on the surface of the framework due to the fact that the framework is unavoidably in contact with air and exploded under the radiance of the sunlight. Therefore the rigidity of the framework may seriously affect and the loading ability of the framework structure also decreases, that may relatively increase the chance of accident. Although the framework assembled by such angle irons can be assembled into various desired shapes by bending the angle irons to adequate shapes in order to fit the connection, it may simultaneously cause a defective that the loading ability of such framework structure would also be greatly lowered.